The inference procedures used here are all based on a sampling
model in which the units are independent and identically
distributed, with each unit being classified with respect to two
categorical variables.

Note that for the risk ratio, the analysis is not symmetric with
respect to the rows and columns of the contingency table. The two
rows define population subgroups, column 0 is the number of
‘events’, and column 1 is the number of ‘non-events’.